Field of the Invention
Embodiments of the present invention relate to a display apparatus, in particular, to an organic light emitting display panel for a display apparatus and a display apparatus.
Description of the Related Art
An organic light emitting display panel is a new type of flat-panel display apparatus, which has many advantages, such as active emission, high brightness, ultrathin thickness, low power consumption, wide angle of view, wide operating temperature range, and the like.
In the organic light emitting display panel, an organic electroluminescent device (OLED) may be divided into two types, i.e., bottom-emitting type and top-emitting type, according to the direction of emergent light. FIG. 1 is a schematic structural view of a conventional bottom-emitting organic electroluminescent device in the prior art, in which the device comprises a reflective cathode 11, an electron transport layer 12, a light emitting layer 13, a hole transport layer 14, a transparent anode 15 and a substrate 16 arranged sequentially in a transmission direction of light. In such device, Indium Tin Oxide (ITO) is generally used as the transparent anode, and the light exits from a side of the device where the substrate provided with ITO material is located, therefore such device is referred to as a Bottom-Emitting device (Bottom-Emitting OLED, BEOLED). In contrast, light of a Top-Emitting device (Top-emitting OLED, TEOLED) exits from a side of the device where a top electrode is located. Correspondingly, FIG. 2 is a schematic structural view of a top-emitting organic electroluminescent device in the prior art, in which the device comprises a cathode 21, an electron transport layer 22, a light emitting layer 23, a hole transport layer 24, a reflective anode 25 and a substrate 26 arranged sequentially in the reverse transmission direction of the light, and the light of the device exits from the cathode 21.
In a conventional bottom-emitting device, the light is restrained to be emitted out of the device through an opening portion provided in an array substrate, which is used for driving the organic light emitting display panel. However, such device has a complicated OLED pixel driving circuit, typically requiring at least two thin film transistors (TFT) and one capacitor, as a result, a majority of light is wasted due to obstruction of the TFT and various electrodes, thereby causing a very low aperture ratio, for example, the light emitted out of the panel in the bottom-emitting device is typically approximately 30-50% of the light emitted from the light emitting layer. Instead, the top-emitting device may solve the shortcoming of low aperture ratio accompanying with the common bottom-emitting device since the top-emitting device emits light from a surface of a top cathode thereof directly, without negative affection on the aperture ratio, thereby facilitating achievement of a large scale, high information content, high display brightness, high resolution, organic flat-panel display.
In the top-emitting device, light is required to exit the device through a cathode of an organic light emitting diode, so it requires that material of the cathode has a relatively high transmittance. With regard to selection of the cathode material in the top-emitting device, there are mainly two types of material, one type of material comprises transparent oxide, for example, Indium Tin Oxide (ITO), and the other type of material comprises metal material. As a kind of transparent electrically conductive material, ITO may reduces light loss in the top emitting process, however, such material has related disadvantages, such as high resistance, complicated sputter process and damage to the organic layer derived from the sputter process, thus affecting display effect. As shown in FIG. 2, the other type of metal material may be plated onto a surface layer of the electron transport layer by a thermal-evaporation method, so as to form a metal cathode. At present, the material used for the metal cathode includes Al, Ag, Al/Ag, Mg/Ag, Ca/Ag, Sm/Ag, and so on. A manufacturing process of the metal cathode is simple, and the evaporation of metal material applies a little damage to the organic layer. However, the thickness of the metal cathode layer is required to be controlled during the evaporation of such metal material. Too thick metal cathode may reduce the transmittance of the device, further affect the display brightness, thereby increasing power consumption for displaying. Based on this, the metal cathode in the top-emitting device is generally provided to be relatively thinner, however, an overall resistance of the thin metal cathode is extremely large, it therefore leads to a relatively high voltage drop. Particularly, the voltage drop across the cathode increases significantly with the increase of dimension thereof, thereby incurring a non-uniform image quality and display characteristic.